Patch 5.4.0 (10-Sep-2013) Nightstalker now increases damage dealt by abilities while stealthed by 50%, up from 25%.

Patch 4.1.0 (26-Apr-2011): Nightstalker now reduces the cooldown of Stealth by 2/4 seconds, and instead of negating the movement penalty from Stealth, it adds a 5/10% movement speed bonus (stacking with other effects) while Stealthed.